120 American Fisheries Society 



first sight seem to be natural and obvious groups are far 

 from being hard and fast lines. For example, what at first 

 blush appears easier to do than to divide animals into para- 

 sitic and non-parasitic forms? An attempt to place the 

 animals with which one is acquainted in one or the other of 

 these groups soon brings one to consider degrees of para- 

 sitism. For example, there are the familiar insect parasites, 

 many of which lead independent lives but find their most 

 congenial habitat in those jungles of hair and feathers which 

 they find on the outsides of mammals and birds. Some of 

 these insects, it is true, as the bot-fly, enact a part of their 

 life history as internal parasites finding favoring conditions 

 in the alimentary canal of the horse, but in their adult stage 

 are as truly children of the light and air as the butterfly. 

 Then, in such a classification, where is the mammal to be 

 placed? During its uterine existence it is one of the best 

 examples of true parasitism to be found in all the empire of 

 nature. Following this important and essential act, though 

 it is played, as it were, before the curtain is raised, conies 

 another in which the young mammal is a highly specialized, 

 but none the less true, ectoparasite. The classifier thus dis- 

 covers, crown of creation though he be, that for a time he 

 himself has been, so far as his method of taking and receiv- 

 ing nourishment is concerned, among the lowly ectoparasites 

 and the lowlier internal parasites. 



Shifting our point of view slightly, it may be remarked 

 that the fauna and flora which are for a greater or less 

 portion of their existence within other animals, are them- 

 selves living things, and their tissues may and do become 

 food for some of the animals which eat them. An example, 

 from many at hand, is a cestode (Rhyuchobothrium impari- 

 spine) the adult stage of which occurs in the winter skate 

 (Raja ocellata) and a few of its near relatives. Glancing 

 over my check-list, I find that I have recorded cysts of this 

 species from no less than 34 species of the marine fishes of 

 New England. Now these 34 species comprise kinds such 

 as silversides, smelt, mackerel, etc., which are eaten by a 



